The less tired I am The less tired I am The less I sleep The less I sleep The more tired I am

+

Lelah
-

-

Tidur

+

+ -

Birth rate
+

+

Population
-

Death rate

 Evaporation  clouds  rain  amount of water  evaporation  …

Sunshine
+

+ +

Earth’s temperature
+

+

Evaporation
+
+

-

A mount of water on earth

+

Clouds
+

Rain





Items that affect other items in the system but are not themselves affected by anything in the system Arrows are drawn from these items but there are no arrows drawn to these items
+

Sunlight reaching each plant Sunlight
+ -

-

Density of plants

 

Systems often respond sluggishly (dgn malas) From the example below, once the trees are planted, the harvest rate can be „0‟ until the trees grow enough to harvest
delay

+ Harvest rate

# of growing trees Planting rate -

-

+





 



There are systems which have more than one feedback loop within them A particular loop in a system of more than one loop is most responsible for the overall behavior of that system The dominating loop might shift over time When a feedback loop is within another, one loop must dominate Stable conditions will exist when negative loops dominate positive loops

Work to do Project Model
+ -

quality of work
-

Work To Do

required workforce

hiring delay + actual workforce

fatigue
+

+

-

overtime hours required

work done
+ + productivity

Level

Rate

Flow arc

Auxiliary

Cause-and-effect arc

Source/Sink Constant


  

Stock, accumulation, or state variable A quantity that accumulates over time Change its value by accumulating or integrating rates Change continuously over time even when the rates are changing discontinuously


 

Flow, activity, movement Change the values of levels The value of a rate is
◦ Not dependent on previous values of that rate ◦ But dependent on the levels in a system along with exogenous influences





 

Arise when the formulation of a level‟s influence on a rate involves one or more intermediate calculations Often useful in formulating complex rate equations Used for ease of communication and clarity Value changes immediately in response to changes in levels or exogenous influences





Source represents systems of levels and rates outside the boundary of the model Sink is where flows terminate outside the system